Concentration of aqueous acetic acid



'A115 14, 1945 H. P. sTAuDlNGER ETAL 2,382,131

CONCENTRATION OF AQUEOUS ACETIC ACID Filed July 15, 1942 'dimmen Patented Aug. 14, 1945 l UNITED STATES PATENT OFFICE CONCENTRATION OFVAQUEOUS ACETIC ACID Hanns Peter Staudinger, Ewell, Karl Heinrich Walter Tuerck, Banstead, and Eric Harvey Brittain, Epsom Downs, England, assignors to The Distillers Company Limited, Edinburgh, Scotland, a British company Application July 15, 1942, Serial No. 451,073 In Great Britain June 17, 1941 i 9 Claims. (Cl. 202-42) This invention is for improvements in or relathyde vapours can leave the top of the column. ing to the concentration of aqueous acetic acid. The acetaldehyde vapours can be condensed or The methods hitherto practiced suffer from the absorbed directly into a parelydehyde scrubbing disadvantage that there is no solvent which is liquid containing traces of sulphuric acid and can able to entrain a satisfactory proportion of water 6 thus be Converted ntO PaIalClehYde Wllicll may be during distillation and which, at the same time, is returned to the concentration processeasily separab1e from the acetic aci@ It has been The following example illustrates the manner proposed to utilise two solvents and to use chem in which the invention may be carried into efin two stages. But such a process has proved to fecl.

be too complicated for industrial use. 1o Into e distillation column A, which is kept un- According to the present invention, paraldeder u Vecuum f 160 mm Hg, 50% by Weight hyde is used as an entraining agent in the distaqueous acetic acid is fed at such a point that lation of dilute aqueous acetic acid. We have the rising vapours moet acurrenlf 0f paralydehyfle found that paraldehyde is able to entrain water flowing down from the top of the column. The in the form of an azeotropic mixture, boiling at l5 VaPOu-TS Which lJ'aSS out at 59 C. and which con- 90 C. /760 mm. Hg, and consisting of 2.5 pari-,s cf tain 2.8 parts by volume of paralydehyde and one paraldehyde and 1 part of water, which separates Dart by Volume of Weller are condensed and the into 2 layers accordingly, paraldehyde layer which separates out is contin- Paraldehyde can be easily depolymerised to uously returned to the column A. acetaldehyde, and thus any excess cf paramchyde From the bottom of the column the hot liquid remaining in the concentrated acetic acid can is withdrawn to the middle of a second column B,

be readily converted into monomeric acetalde- Which Works uli normal Pressure, und the reluX hyde Which is either removed as such or converted depl'llegmatol of Which iS S0 regulated that the into acetic acid by oxidation. temperature of the vapours leaving the top is The accompanying sheet of drawings illus- 11015 more than 25 C The vapours ure c011- trates the process according to the present invcndensed and led into a receiver where they are tion, the various legends indicating the various absorbed by Parelydehyde Containing 0.1% by devices employed and the nature of the various weight of sulphuric acid.

fluids ilowing through the apparatus, The liquid which leaves the bottom of the sec- In carrying out the process of our invention the ond column B iS Pure glacial acetic acid.

aqueous acetic acid, which must be free from The method of this invention is especially usestrong acids or other substances which cause deful when combined with an extraction process in polymerisation of the paraldehyde, is distilled which paraldehyde has been employed as the eX- with about the calculated amount of paraldehyde tracting agent for the extraction of acetic acid corresponding to the water to be removed so that, 35 from aqueous solutions or if an excess of paraldeat the top of the rectiiying column A, a mixture hyde has been used so as to effect a quick and of paraldehyde and Water is obtained, while at ready removal of the water at the top of the the bottom of the column B the water-free acid column.

is withdrawn and, if it contains any residual What we claim is:

paraldehyde, this is fed into a second small coll. A method 0f dehydratiug aqueous acetic umn in which the paralydehyde is depolymerised acid which comprises the step of distilling off the and distilled oi as acetaldehyde which, because Water in azeotropic admixture with paraldehydeof its loW boiling point, is easily separable from 2. A method according to claim 1 wherein any the acetic acid. Pure acetic acid is drawn oli as excess of paraldehyde remaining in the dehyvapour or liquid from one of the lower parts of drated acetic acid is removed by heating the mixthe second column B. We prefer to eiiect the ture to such a temperature that depolymerisation azeotropic distillation under such a vacuum that thereof occurs, the resulting acetaldehyde being distillation occurs at a temperature :below 80 C. removed by distillation.

so that there is no possibility of the paraldehyde 3. A method according to claim 1 wherein the depolymerising. The depolymerisation of the removal of water is effected under a reduced presresidual paraldehyde, if any, may be effected in a sure such that the distillation temperature resecond column B by means of small amounts of mains below 80 C.

sulphuric acid running down the column or by 4. A method of dehydrating aqueous acetic acid slowly fractionating the acetic acid-paralydehyde wherein aqueous acetic acid is fed to a. distillation mixture .under such conditions that only acetaldecolumn in which paralydehyde is :flowing down,

the mixed vapours of Water and paraldehyde are withdrawn at the top of the column, the acetic acid, containing paraldehyde, being Withdrawn from the base of said column and fed to a second column tted with a reflux dephlegmator so regulated that only acetaldheyde is removed, the glacial acetic acid being Withdrawn from the base of the second said column.

5. A method of dehydrating aqueous acetic acid Which comprises heating said aqueous acetic acid in a distillation column with paraldehyde, removing an azeotropic mixture consisting of water and paraldehyde, removing from the base of the column an anhydrous mixture of acetic acid and paralydehyde, heating said anhydrous mixture to cause depolymerisation of the contained paraldehyde to acetaldehyde and absorbing said acetaldehyde in liquid paraldehyde containing an acidic polymerising agent to regenerate paraldehyde.

6. A method of dehydrating aqueous acetic acid which comprises heating said aqueous acetic acid in a distillation column with paraldehyde, remov-v ing an azeotropic mixture consisting of Waterand paraldehyde, removing from the base of the column an anhydrous mixture of acetic acid and paraldehyde, heating said anhydrous mixture with an acidic depolymerising agent to cause depolymerisation of the containedparaldehyde to acetaldehyde and absorbing said acetaldehyde in liquid paraldehyde containing an acidic polymer- '3o ising agent to regenerate paraldehyde.

7. A method of dehydrating aqueous acetic acid which comprises heating said aqueous acetic acid in a distillation column with paraldehyde, removing an azeotropic mixture consisting of Water and paraldehyde, removing from the base of the column an anhydrous mixture of acetic acid and paraldehyde, heating said anhydrous mixture with sulphuric acid to cause depolymerisation of the contained paraldehyde to acetaldehyde and absorbing said acetaldehyde in liquid paraldehyde containing an acidic polymerising agent to regen- 'erate paraldehyde.

8. A method of dehydrating aqueous acetic acid which comprises heating said aqueous acetic acid in a distillation column with paraldehyde,remov ing an azeotropic mixture consisting of water and paraldehyde, removing from the base of the column an anhydrous mixture of acetic acid and paraldehyde, and heating said anhydrous mixture with an acidic depolymerising agent to cause depolymerisation of the contained paraldehyde to acetaldehyde.

9. A method of dehydrating aqueous acetic acid which comprises heating said aqueous acetic acid in a distillation column with paraldehyde, removing an azeotropic mixture consisting of water and paraldehyde, removing from the base of the col umn an anhydrous mixture of acetic acid and paraldehyde, and heating said anhydrous mixture with sulphuric acid to cause depolymerisation of the contained paraldehyde to acetaldehyde.

HANNS PETER STAUDINGER. KARL HEINRICH WALTER TUERCK. ERIC HARVEY BRIT'IAIN. 

